Data were collected over the period between May and September 2002 from 70 IDUs examined while in police custody in Bristol, United Kingdom. Participants were asked a series of questions about their injecting history, whether they had ever experienced a needle breaking while injecting, and, if so, the details of the incident. Results show that 20 percent of the participants reported that they had experienced a needle breaking on one or more occasion while injecting. Possible causes of needles breaking included faulty or damaged needles, hardened veins associated with chronic inflammation or sudden movement at the injection site; examples of each of these were cited by IDUs in this survey. Sixty percent of the broken needles were recovered, 4 by surgical intervention, and 10 as a result of direct action by the individual. The other nine were not retrieved and remained within the body. Retained broken needles can lead to local complications, such as infection, but they also have the potential to embolize and cause central complications. The IDUs surveyed had been injecting drugs for an average of 6.4 years. The approximate incidence of broken needles was one for every 20 years of injecting. This survey has demonstrated that many IDUs are likely to experience (directly or indirectly) incidents involving broken needles during the course of their injecting careers. Subsequent needle embolization may be more common than appears, since drug abusers tend to avoid hospitals unless seriously ill. It is recommended that harm minimization guidance should include advice about this potential hazard. Written guidance should emphasize the need for early action by IDUs to retrieve broken needles. 2 tables, 15 references, 1 appendix